title	description	ms.topic	ms.date	ms.devlang	ms.custom
Create a function in Go or Rust using Visual Studio Code - Azure Functions	Learn how to create a Go function as an Azure Functions custom handler, then publish the local project to serverless hosting in Azure Functions using the Azure Functions extension in Visual Studio Code.	quickstart	12/4/2020	golang, rust	mode-api

Quickstart: Create a Go or Rust function in Azure using Visual Studio Code

[!INCLUDE functions-language-selector-quickstart-vs-code]

In this article, you use Visual Studio Code to create a custom handler function that responds to HTTP requests. After testing the code locally, you deploy it to the serverless environment of Azure Functions.

Custom handlers can be used to create functions in any language or runtime by running an HTTP server process. This article supports both Go and Rust.

Completing this quickstart incurs a small cost of a few USD cents or less in your Azure account.

Configure your environment

Before you get started, make sure you have the following requirements in place:

Go

An Azure account with an active subscription. Create an account for free.
Visual Studio Code on one of the supported platforms.
The Azure Functions extension for Visual Studio Code.
The Azure Functions Core Tools version 3.x. Use the func --version command to check that it is correctly installed.
Go, latest version recommended. Use the go version command to check your version.

Rust

An Azure account with an active subscription. Create an account for free.
Visual Studio Code on one of the supported platforms.
The Azure Functions extension for Visual Studio Code.
The Azure Functions Core Tools version 3.x. Use the func --version command to check that it is correctly installed.
Rust toolchain using rustup. Use the rustc --version command to check your version.

Create your local project

In this section, you use Visual Studio Code to create a local Azure Functions custom handlers project. Later in this article, you'll publish your function code to Azure.

Choose the Azure icon in the Activity bar, then in the Azure: Functions area, select the Create new project... icon.
Choose a directory location for your project workspace and choose Select.

[!NOTE] These steps were designed to be completed outside of a workspace. In this case, do not select a project folder that is part of a workspace.
Provide the following information at the prompts:
- Select a language for your function project: Choose Custom.
- Select a template for your project's first function: Choose HTTP trigger.
- Provide a function name: Type HttpExample.
- Authorization level: Choose Anonymous, which enables anyone to call your function endpoint. To learn about authorization level, see Authorization keys.
- Select how you would like to open your project: Choose Add to workspace.
Using this information, Visual Studio Code generates an Azure Functions project with an HTTP trigger function. You can view the local project files in the Explorer. To learn more about files that are created, see Generated project files.

Create and build your function

The function.json file in the HttpExample folder declares an HTTP trigger function. You complete the function by adding a handler and compiling it into an executable.

Go

Press Ctrl + N (Cmd + N on macOS) to create a new file. Save it as handler.go in the function app root (in the same folder as host.json).

In handler.go, add the following code and save the file. This is your Go custom handler.

package main

import (
    "fmt"
    "log"
    "net/http"
    "os"
)

func helloHandler(w http.ResponseWriter, r *http.Request) {
    message := "This HTTP triggered function executed successfully. Pass a name in the query string for a personalized response.\n"
    name := r.URL.Query().Get("name")
    if name != "" {
        message = fmt.Sprintf("Hello, %s. This HTTP triggered function executed successfully.\n", name)
    }
    fmt.Fprint(w, message)
}

func main() {
    listenAddr := ":8080"
    if val, ok := os.LookupEnv("FUNCTIONS_CUSTOMHANDLER_PORT"); ok {
        listenAddr = ":" + val
    }
    http.HandleFunc("/api/HttpExample", helloHandler)
    log.Printf("About to listen on %s. Go to https://127.0.0.1%s/", listenAddr, listenAddr)
    log.Fatal(http.ListenAndServe(listenAddr, nil))
}

Press Ctrl + Shift + ` or select New Terminal from the Terminal menu to open a new integrated terminal in VS Code.
Compile your custom handler using the following command. An executable file named handler (handler.exe on Windows) is output in the function app root folder.
```
go build handler.go
```

Rust

Press Ctrl + Shift + ` or select New Terminal from the Terminal menu to open a new integrated terminal in VS Code.
In the function app root (the same folder as host.json), initialize a Rust project named handler.
```
cargo init --name handler
```
In Cargo.toml, add the following dependencies necessary to complete this quickstart. The example uses the warp web server framework.
```
[dependencies]
warp = "0.3"
tokio = { version = "1", features = ["rt", "macros", "rt-multi-thread"] }
```

In src/main.rs, add the following code and save the file. This is your Rust custom handler.

use std::collections::HashMap;
use std::env;
use std::net::Ipv4Addr;
use warp::{http::Response, Filter};

#[tokio::main]
async fn main() {
    let example1 = warp::get()
        .and(warp::path("api"))
        .and(warp::path("HttpExample"))
        .and(warp::query::<HashMap<String, String>>())
        .map(|p: HashMap<String, String>| match p.get("name") {
            Some(name) => Response::builder().body(format!("Hello, {}. This HTTP triggered function executed successfully.", name)),
            None => Response::builder().body(String::from("This HTTP triggered function executed successfully. Pass a name in the query string for a personalized response.")),
        });

    let port_key = "FUNCTIONS_CUSTOMHANDLER_PORT";
    let port: u16 = match env::var(port_key) {
        Ok(val) => val.parse().expect("Custom Handler port is not a number!"),
        Err(_) => 3000,
    };

    warp::serve(example1).run((Ipv4Addr::LOCALHOST, port)).await
}

Compile a binary for your custom handler. An executable file named handler (handler.exe on Windows) is output in the function app root folder.
```
cargo build --release
cp target/release/handler .
```

Configure your function app

The function host needs to be configured to run your custom handler binary when it starts.

Open host.json.
In the customHandler.description section, set the value of defaultExecutablePath to handler (on Windows, set it to handler.exe).
In the customHandler section, add a property named enableForwardingHttpRequest and set its value to true. For functions consisting of only an HTTP trigger, this setting simplifies programming by allow you to work with a typical HTTP request instead of the custom handler request payload.

Confirm the customHandler section looks like this example. Save the file.

"customHandler": {
  "description": {
    "defaultExecutablePath": "handler",
    "workingDirectory": "",
    "arguments": []
  },
  "enableForwardingHttpRequest": true
}

The function app is configured to start your custom handler executable.

Run the function locally

You can run this project on your local development computer before you publish to Azure.

In the integrated terminal, start the function app using Azure Functions Core Tools.
```
func start
```
With Core Tools running, navigate to the following URL to execute a GET request, which includes ?name=Functions query string.

http://localhost:7071/api/HttpExample?name=Functions
A response is returned, which looks like the following in a browser:
Information about the request is shown in Terminal panel.
Press Ctrl + C to stop Core Tools.

After you've verified that the function runs correctly on your local computer, it's time to use Visual Studio Code to publish the project directly to Azure.

[!INCLUDE functions-sign-in-vs-code]

Compile the custom handler for Azure

In this section, you publish your project to Azure in a function app running Linux. In most cases, you must recompile your binary and adjust your configuration to match the target platform before publishing it to Azure.

Go

In the integrated terminal, compile the handler to Linux/x64. A binary named handler is created in the function app root.

macOS
```
GOOS=linux GOARCH=amd64 go build handler.go
```
Linux
```
GOOS=linux GOARCH=amd64 go build handler.go
```
Windows
```
set GOOS=linux
set GOARCH=amd64
go build handler.go
```
Change the defaultExecutablePath in host.json from handler.exe to handler. This instructs the function app to run the Linux binary.

Rust

Create a file at .cargo/config. Add the following contents and save the file.
```
[target.x86_64-unknown-linux-musl]
linker = "rust-lld"
```

In the integrated terminal, compile the handler to Linux/x64. A binary named handler is created. Copy it to the function app root.

rustup target add x86_64-unknown-linux-musl
cargo build --release --target=x86_64-unknown-linux-musl
cp target/x86_64-unknown-linux-musl/release/handler .

If you are using Windows, change the defaultExecutablePath in host.json from handler.exe to handler. This instructs the function app to run the Linux binary.
Add the following line to the .funcignore file:
```
target
```
This prevents publishing the contents of the target folder.

Publish the project to Azure

In this section, you create a function app and related resources in your Azure subscription and then deploy your code.

Important

Publishing to an existing function app overwrites the content of that app in Azure.

Choose the Azure icon in the Activity bar, then in the Azure: Functions area, choose the Deploy to function app... button.
Provide the following information at the prompts:
- Select folder: Choose a folder from your workspace or browse to one that contains your function app. You won't see this if you already have a valid function app opened.
- Select subscription: Choose the subscription to use. You won't see this if you only have one subscription.
- Select Function App in Azure: Choose + Create new Function App (advanced).
  
  [!IMPORTANT] The advanced option lets you choose the specific operating system on which your function app runs in Azure, which in this case is Linux.
- Enter a globally unique name for the function app: Type a name that is valid in a URL path. The name you type is validated to make sure that it's unique in Azure Functions.
- Select a runtime stack: Choose Custom Handler.
- Select an OS: Choose Linux.
- Select a hosting plan: Choose Consumption.
- Select a resource group: Choose + Create new resource group. Enter a name for the resource group. This name must be unique within your Azure subscription. You can use the name suggested in the prompt.
- Select a storage account: Choose + Create new storage account. This name must be globally unique within Azure. You can use the name suggested in the prompt.
- Select an Application Insights resource: Choose + Create Application Insights resource. This name must be globally unique within Azure. You can use the name suggested in the prompt.
- Select a location for new resources: For better performance, choose a region near you.The extension shows the status of individual resources as they are being created in Azure in the notification area.
:::image type="content" source="../../includes/media/functions-publish-project-vscode/resource-notification.png" alt-text="Notification of Azure resource creation":::
When completed, the following Azure resources are created in your subscription:

[!INCLUDE functions-vs-code-created-resources]

A notification is displayed after your function app is created and the deployment package is applied.
Select View Output in this notification to view the creation and deployment results, including the Azure resources that you created. If you miss the notification, select the bell icon in the lower right corner to see it again.

[!INCLUDE functions-vs-code-run-remote]

[!INCLUDE functions-cleanup-resources-vs-code.md]

Next steps

[!div class="nextstepaction"] Learn about Azure Functions custom handlers

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Quickstart: Create a Go or Rust function in Azure using Visual Studio Code

Configure your environment

Go

Rust

Create your local project

Create and build your function

Go

Rust

Configure your function app

Run the function locally

Compile the custom handler for Azure

Go

macOS

Linux

Windows

Rust

Publish the project to Azure

Next steps

Files

create-first-function-vs-code-other.md

Latest commit

History

create-first-function-vs-code-other.md

File metadata and controls

Quickstart: Create a Go or Rust function in Azure using Visual Studio Code

Configure your environment

Create your local project

Create and build your function

Configure your function app

Run the function locally

Compile the custom handler for Azure

Publish the project to Azure

Next steps